mitt romney and president obama are set to square off tonight in denver for the first of three presidential debates. you can catch it all right here live on cnbc beginning at 8:00 p.m. eastern. i'll be hosting the pre and post coverage along with carl quintanilla. of course, john harwood will also be with us. he's live on the ground in denver. he's here with a preview. over to you, john. >> hey, maria. it's important to remember this election isn't over. if you look at the new polls that we came out with last night and this morning, mitt romney's only trailing by three points nationally. that's down from a five-point margin a couple weeks ago. he's 9/11 florieven in florida,. he still trails in ohio by five points. that's a big problem. he needs to win the state of ohio. that just shows he has an opportunity tonight. three other big economic issues they're going to be talking about, first of all, on taxes. mitt romney hasosed a 20% across the board rate cut for individuals, but he hasn't specified how he's going to pay for that without increasing the deficit or increasing the burden on midd